Which sentence is an example of faulty coordination?

a. manufacturing has declined in philadelphia since 1950, but it is still an important part of the city’s economy.

b. service industries have begun to play an important role in philadelphia, and the city’s economy is more complex.

c. philadelphia was once one of the world’s leading manufacturing cities, but other manufacturing cities have since surpassed it.

d. the port of philadelphia handles millions of ton of cargo each year, and it is host to some 5,000 ships.